Hang Sơn Đoòng ('cave of the mountain river or 'mountain cave of Đoòng in Vietnamese), also known asSơn Đoòng cave (often without the tone marks) is a solutional cave in Phong Nha-Kẻ Bàng National Park, Bố Trạch District, Quảng Bình Province, Vietnam. As of 2009 it has the largest known cave passage cross-section in the world, and is located near the Laos–Vietnam border. Inside is a large, fast-flowing subterranean river. It was formed in Carboniferous/Permian limestone.
Hang Sơn Đoòng was found by a local man named Hồ Khanh in 1991. The whistling sound of wind and roar of a rushing stream in the cave heard through the entrance as well as the steep descent prevented the local people from entering the cave. Only in 2009 did the cave become internationally known after a group of scientists from the British Cave Research Association, conducted a survey in Phong Nha-Kẻ Bàng from 10 to 14 April 2009. Their progress was stopped by a large, 60-metre (200 ft) high calcitewall, which was named the Great Wall of Vietnam. It was traversed in 2010 when the group reached the end of the cave passage.
According to the Limberts, the cave is five times larger than nearby caves like Phong Nha Cave and Hang En, the third largest cave in the world previously considered the biggest cave in Vietnam. The main passage in Sơn Đoòng is more than 5 kilometres (3.1 mi) long, 200 metres (660 ft) high and 150 metres (490 ft) wide. With these dimensions, Sơn Đoòng overtook Deer Cave in Malaysia in 2009 to take the title of the world's largest cave. The cave runs for approximately 9 kilometres (5.6 mi) and is punctuated by 2 large dolines, which are areas where the ceiling of the cave has collapsed. The dolines allow sunlight to enter sections of the cave and has resulted in the growth of trees as well as other vegetation.
The cave contains some of the tallest known stalagmites in the world, which are up to 70 m tall. Behind the Great Wall of Vietnamwere found cave pearls the size of baseballs, an abnormally large size.
In early August 2013, the first tourist group explored the cave on a guided tour at a cost of US$3,000 each. Permits are required to access the cave and are made available on a limited basis. Only 500 permits were issued for the 2015 season, which runs from February to August. After August, heavy rains cause river levels to rise and make the cave largely inaccessible.
Less people have seen the inside of Hang Son Doong than have stood on the summit of Mount Everest. Therefore,after collecting documents and informaion from many different sources we officially recommend that Son Doong Cave is World's largest natural cave to promote it all over the world and will award world record certificate for "Son Doong - World's Largest Natural Cave" to Vietnam.
Source of images: Internet